Thermoplastic vulcanizates (“TPV”s) formed from blends of crosslinked rubber and thermoplastic are known in the art. Morphologically, TPV are characterized by the presence of finely dispersed, micro-sized, rubber particles in a continuous thermoplastic matrix. The rubber phase is vulcanized with suitable curatives, typically by a dynamic vulcanization process. Compared with conventional, non-vulcanized, thermoplastic elastomers (TPEs), TPV materials exhibit better properties, such as heat resistance, oil resistance, and elastic recovery. Compared with thermoset rubbers, TPV materials have the advantage of thermoplastic processability and recyclability. TPVs have also gained wide acceptance as a replacement of both thermoset rubbers and flexible PVC (polyvinylchloride) in a variety of applications.
The physical properties of TPVs are affected by many factors, including the molecular structure of the rubber phase, the properties of the thermoplastic phase, the cure level, and the presence of fillers. Among them, the selection of the rubber phase is considered to have the largest impact on the final properties of the TPV. Ethylene-propylene-diene (EPDM) elastomers are the most widely used rubber in TPV formulations. The molecular microstructural features of EPDM, such as comonomer content, molecular weight, molecular weight distribution, diene content, and level of long chain branching (LCB), have significant influence on the final physical properties of the TPV. There is a need for new TPV formulations with improved dispersion of the rubber phase (more uniform dispersion of the rubber phase, and the rubber particles are smaller with increased interfacial area).
International Publication WO2009/123609 discloses a process for preparing a thermoplastic vulcanizate, the process comprising the following: charging a reactor with an olefinic copolymer rubber; charging the reactor, contemporaneously or sequentially with respect to the rubber, with a thermoplastic resin, an oil, and a cure system; melt mixing the rubber, the thermoplastic resin, the oil, and the cure system; and dynamically vulcanizing the rubber. The olefinic copolymer rubber is characterized by the following: a) a multimodal molecular weight, b) an average branching index of greater than 0.8, c) includes less than 10 parts by weight oil per 100 parts by weight rubber, d) includes less than 1 parts by weight non-rubber particulate, per 100 parts by weight rubber, and e) is in the form of granules having a particle size less than 8 mm.
U.S. Publication 2008/0033089 discloses a thermoplastic vulcanizate composition comprising a dynamically-cured rubber; from about 20 to about 300 parts, by weight, of a thermoplastic resin per 100 parts by weight rubber, and from about 30 to about 250 parts, by weight, additional oil per 100 parts by weight rubber. The rubber comprises a multimodal polymer composition cured with a curing agent. The multimodal polymer composition comprises 45 to 75 weight percent of a first polymer fraction, and 25 to 55 weight percent of a second polymer fraction, each comprising ethylene, a C3-C10 alpha-olefin, and a nonconjugated diene. The polymer fractions were polymerized using a Ziegler-Natta catalyst system, and the first polymer fraction has a Mooney viscosity of greater than, or equal to, about 150 ML(1+4 at 125° C.), and the second polymer fraction has a Mooney viscosity of about 20 ML to about 120 ML; and about 10 phr to about 50 phr of an extender oil.
Additional TPV and/or other formulations are described in the following: U.S. Pat. No. 7,655,727, 6,121,383, 4,130,535, 4,311,628, 4,593,062, U.S. 2007/0129493 A1, U.S. 2006/0199910 A1 (now U.S. Pat. No. 7,579,408), and EP0751182B1.
However, as discussed above, there is a need for new TPV with improved dispersion of the rubber. There is a further need for TPV formulations that have improved low temperature oil retention, and improved surface qualities. These needs have been met by the following invention.